net: rbridge: no need to cast

rbr->br and br jave the exact same type

Signed-off-by: William Dauchy <william@gandi.net>
Signed-off-by: Ahmed Amamou <ahmed@gandi.net>
net: rbridge: use unsigned for non-negative loop

Signed-off-by: William Dauchy <william@gandi.net>
Signed-off-by: Ahmed Amamou <ahmed@gandi.net>